High speed stable light emitting semiconductor device with low threshold current

Abstract

A highly efficient light emitting semiconductor device which is stable at high speeds and has a low threshold current comprising a first semiconductor layer of a first conductive type; a second semiconductor layer of the second conductive type which is different from the first conductive type; an active layer composed of laminated semiconductor layers of the quantum well structure interposed between the first and second semiconductor layers and having a narrower effective energy band gap than the first and second semiconductor layers and a diffraction grading formed in either one of the first or second semiconductor layers.

I claim: 
     
       1. A light emitting double heterojunction semiconductor device of injection type comprising: a first semiconductor layer of a first conductive type;   a second semiconductor layer of a second conductive type which is different from the first conductive type;   an active layer composed of laminated semiconductor layers of the quantum well structure interposed and extended beneath the first and second semiconductor layers and having a narrower effective energy band gap than those of the first and second semiconductor layers;   a first electrode formed on the surface of the first semiconductor layer opposite a surface facing the active layer and a second electrode formed on the surface of the second semiconductor layer opposite a surface facing the active layer such that a portion of the active layer sandwiched between the first and second electrodes forms an active region for laser oscillation: and   a pair of diffraction gratings formed in either one of the first and second semiconductor layers such that a grating is positioned at each side of the active region,   whereby said active layer functions as the active region and as a waveguide region.   
     
     
       2. A light emitting double heterojunction semiconductor device as claimed in claim 1, wherein the first electrode is formed on a predetermined area of the outer surface of either one of the first and second semiconductor layers, said diffraction gratings being formed in said one of said first and second semiconductor layers at opposite sides of said predetermined area. 
     
     
       3. A light emitting double heterojunction semiconductor device as claimed in claim 2, wherein either one of the first and second semiconductor layers is composed of two semiconductor layers of the same conductive type of which the energy band gaps are different from each other, the interface of these two semiconductor layers being formed to present a regular waveform at said portions to thereby form diffraction gratings. 
     
     
       4. A light emitting double heterojunction semiconductor device as claimed in claim 2, wherein the first semiconductor layer is composed of a buffer layer formed on a semiconductor substrate of the same conductive type as the first semiconductor layer, the second electrode being formed on the outer surface of the semiconductor substrate, and wherein the second semiconductor layer is composed of a cladding layer and a contact layer of the same conductive type with each other, the first electrode being formed on the contact layer. 
     
     
       5. A light emitting double heterojunction semiconductor devices as claimed in claim 4, wherein the diffraction grating is formed in said second semiconductor layer. 
     
     
       6. A light emitting double heterojunction semiconductor device as claimed in claim 5, wherein the cladding layer is composed of two semiconductor layers of which the energy band gaps are different from each other and the diffraction grating is formed at the interface therebetween. 
     
     
       7. A light emitting double heterojunction semiconductor device as claimed in claim 4, the buffer layer is composed of two semiconductor layers of which the energy band gaps are different from each other and the diffraction grating is formed at the interface therebetween. 
     
     
       8. A light emitting double heterojunction semiconductor device as claimed in claim 4, wherein the active layer is composed of two kinds of thin semiconductor layers having a different energy band gap from each other and laminated on each other. 
     
     
       9. A light emitting double heterojunction semiconductor device as claimed in claim 4, wherein the semiconductor substrate is composed of InP. 
     
     
       10. A light emitting double heterojunction semiconductor device as claimed in claim 9, said active layer is composed of laminated layers of InP and In 0 .53 Ga 0 .47 As. 
     
     
       11. A light emitting double heterojunction semiconductor device as claimed in claim 9, wherein the active layer is composed of laminated layers of In 0 .52 Ga 0 .48 As and In 0 .53 Ga 0 .47 As. 
     
     
       12. A light emitting double heterojunction semiconductor device as claimed in claim 9, wherein the semiconductor layers between which the diffraction grating is formed are composed respectively of InP and InGaAsP. 
     
     
       13. A light emitting double heterojunction semiconductor devices as claimed in claim 4, wherein the semiconductor substrate is composed of GaAs. 
     
     
       14. A light emitting double heterojunction semiconductor device as claimed in claim 13, wherein the active layer is composed of laminated layers of GaAs and Al x  Ga 1-x  As (0<×<1). 
     
     
       15. A light emitting double heterojunction semiconductor devices as claimed in claim 14, wherein the semiconductor layers between which the diffraction grating is formed are composed respectively of Al x  Ga 1-x  As and Al y  Ga 1-x  As (x≠y). 
     
     
       16. A light emitting double heterojunction semiconductor device as claimed in claim 2, further comprising a semiconductor substrate on which the first semiconductor layer is formed as the buffer layer and a second electrode is formed on the outer surface of the semiconductor substrate, said second semiconductor layer being composed of a cladding layer and a contact lay of the same conductive type with each other, a first electrode being formed on the outer surface of the contact layer, and wherein the contact layer is formed only on a predetermined surface area of the cladding layer and the cladding layer presents regular waveform at the outer surface area which is not covered by the contact layer, whereby forming diffraction gratings. 
     
     
       17. A light emitting double heterojunction semiconductor devices as claimed in claim 16, wherein the cladding layer is composed of two semiconductor layers of which the energy band gaps are different from each other and the diffraction grating is formed at the interface therebetween. 
     
     
       18. A light emitting double heterojunction semiconductor device as claimed in anyone of claim 16, wherein the semiconductor substrate is composed of InP. 
     
     
       19. A light emitting double heterojunction semiconductor device as claimed in claim 18, the active layer is composed of laminated layers of InP and In 0 .53 Ga 0 .47 As. 
     
     
       20. A light emitting double heterojunction semiconductor device as claimed in claim 16, wherein the active layer is composed of laminated layers of In 0 .52 Al 0 .48 As and In 0 .53 Ga 0 .47 As. 
     
     
       21. A light emitting double heterojunction semiconductor device as claimed in anyone of claim 16, wherein the semiconductor substrate is composed of GaAs. 
     
     
       22. A light emitting double heterojunction semiconductor device as claimed in claim 21, wherein the semiconductor layers between which the diffraction grating is formed are composed respectively of Al x  Ga 1-x  As and Al y  Ga 1-y  As (x≠y).